Combined detectors of charged particles are described based on zinc selenide (ZnSe(Te)) crystals, silicon photodiodes and charge-sensitive amplifiers. ZnSe(Te) scintillators are characterized by high alpha to beta ratio (~1.0), good scintillation efficiency (up to 22%), and high radiation stability (up to 100 Mrad), together with good spectral matching with silicon PIN photodiodes. The signals coming from the photodiode in the two modes (photoreceiver and semiconductor detector) differ in the amplitude values and pulse duration, which opens new possibilities for development and application of such combined detectors

Chernikov, V.V.

Danshin, E.A.

Gal’chinetskii, L.P.

Katrunov, K.A.

Ryzhikov, V.D.

Starzhinskiy, N.G.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

COMBINED DETECTORS OF CHARGED PARTICLES BASED ON ZINC SELENIDE SCINTILLATORS AND SILICON PHOTODIODESV.D. Ryzhikov, L.P. Gal’chinetskii, N.G. Starzhinskiy, E.A. Danshin, K.A. Katrunov, V.V. ChernikovSTC for Radiation InstrumentsConcern “Institute for Single Crystals” of the National Academy of sciences of Ukraine60 Lenin Ave., 61001, Kharkov, Ukrainee-mail: stcri@isc.kharkov.comCombined detectors of charged particles are described based on zinc selenide (ZnSe(Te)) crystals, silicon photodi-odes and charge-sensitive amplifiers. ZnSe(Te) scintillators are characterized by high alpha to beta ratio (~1.0), good scintillation efficiency (up to 22%), and high radiation stability (up to 100 Mrad), together with good spectral matching with silicon PIN photodiodes. The signals coming from the photodiode in the two modes (photoreceiver and semiconductor detector) differ in the amplitude values and pulse duration, which opens new possibilities for de-velopment and application of such combined detectors.PACS number: 29.27.Fa1  INTRODUCTIONAmong the most efficient methods used for detec-tion and identification of charged particles and products of nuclear reactions occurring on target nuclei in mixed fields in reactors and accelerators, very promising is the use  of  combined  detectors  (CD)  based  on  inorganic scintillators and silicon photodiodes (PD). Such solid-state  combined  detectors  have  acquired  a  trademark SELDI  (ScintiELectronic  Detectors  of  Ionizing  radia-tion), which is commonly used in CIS countries. Their Western analogs are generally known as Siswich [1]. In this paper, a number of variants of such detectors are described, which are used for separate detection of neu-trons and gamma-radiation in mixed fields, detection of low- and high-energy gamma-radiation, as well as inter-nal conversion electrons together with the accompany-ing gamma-radiation. In this paper, we present for the first time a new SELDI type CD for separate detection of light and heavy charged particles in the mixed fields.2  EXPERIMENTAL PROCEDURESFor the use as part of CD, we have chosen ZnSe(Te) crystals grown as described earlier [2]. From the single crystals, plates were cut, of dimensions 10x10 mm and thickness 0.8-1.0 mm. The output windows of the plates (facing  the  photosensitive  surface  of  PD)  were  made opaque, and the input ones (facing the charged particle flux) were polished. The plates were packed in contain-ers made of Teflon with collimator windows on the in-put windows for transmission of the incoming charged particles.  In  measurements  with  internal  conversion electrons  (ICE),  the  distance  between  the  radiation source  and  the  collimator  was  not  less  than  20 mm, while for detection of alpha-particles the sources were located  just  upon  the  collimator.  The  measurements were carried out at room temperature using an immer-sion contact, using Vaseline oil as an immersion sub-stance. To protect Si-PIN-PD from the low-energy gam-ma- and X-ray radiation, light transducers made of inor-ganic crystals were occasionally used.Comparative characteristics of ZnSe(Te) and CsI(Tl) are given in Table 1.Table 1. Characteristics of scintillators produced by Concern “Institute for Single Crystals”Cristal λmax, nm τ, µs α, cm-1 Zeff. S, rel.un. Tmax, КZnSe(Te) 600-620630-6402-20>20 0,05-0,15 33100170 400-450CsI(Tl) 550 0,63-1 > 0.05 54 100 350-400Designations: λmax – maximum position in the radioluminesce spectra, τ - decay time, α - scintillation light absorp-tion coefficient, Zeff – effective atomic number, S – relative light output, Tmax – maximum operation temperature.Measurements  of  CD spectrometric  characteristics were  carried  out  using  ICE  sources  109Cd,  137Cs  and 207Bi, as well as alpha-sources 239Pu, 241Am and 226Ra and X-ray  and  gamma-quanta  sources  55Fe,  241Am,  57Co, 137Cs,  22Na at working temperature of 294 K. As pho-toreceivers,  we  used  PD  obtained  from  Hamamatsu (S3590-01)  and  “Porog”  type  PD  from  NCB  Ritm, Chernovtsy, Ukraine. Comparative characteristics of the PD used are presented in Table 2.Table 2. Parameters of Si-PIN-photodiodesParameters S3590-01 «Porog» NPO «BІТ»Light  sensetive area, mm2 10х10 10х10 ∅25Dark current, nA 1,5 1,6Bias voltage, V 30 30 50Capacitance, pF 70 67 220 ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 174-176.174Sensitivity  for  λ=540 nm, A/W 0,31 0,26 0,32The spectral sensitivity maximum of Si-PIN-PD is in the region of 800-900 nm, ensuring 70 % matching with the spectral characteristics of ZnSe(Te) crystal radiolu-minescence.  Very  high  requirements  were  put  to  all links of the spectrometric circuit chain, especially to the charge-sensitive  pre-amplifier  (CSPA)  comprising  a charge-sensitive section with a field transistor at the in-put and elements of the detector power supply. Our ex-periments have shown that the lowest noise level can be obtained with KP341A field  transistor  (the  calculated intrinsic noise level is < 400 electrons at Si-PIN-PD ca-pacitance of 70 pF. Signal ratio at the PD output was about 1:10, both in the photoreceiver mode and in the semiconductor detector mode.After the pre-amplifier, additional amplification and signal shaping was ensured by an active filter-amplifier of  1101  type,  with  input  shaping  times  up  to  40 μs. Scintillation characteristics of ZnSe(Te) single crystals were studied at shaping time τ1 = 15 μs, and this value was put as τ2 = 0.1 μs for Si-PIN-PD used as a spectro-metric detector.Spectrometric studies were carried out using a multi-channel analyzer based on a Notebook Pentium PC in combination with an original ADC (developed at STC RI in the PCMCIA standard). The energy consumption was low, with a power supply of +5 V effectuated from the PC cable.  This complex of  developments allowed the spectrometer to be small-sized.3  RESULTS AND DISCUSSIONPulse amplitude spectra recorded by scintielectronic detectors using the studied crystals and Si-PIN-PD were measured in the amplitude scale of gamma-quanta. The noise  level  of  the  semiconductor  Si-PIN-PD  detector (SCD) allowed to clearly detect KX-quanta of 55Fe (see Fig. 1). Analysis of these spectra and calculations of the noise level for PD-CSPA system show that the intrinsic noise level of the system is 420 electrons.Counting rate,R.U.Channel number100020003000400050006000700080000 50 100 150 20055FeFe Kβ1β2(6.490 keV)number)Fe Kα1(5.899 keV)R=42 %Fig. 1. Spectrum of 55Fe KX-quanta obtained using a semiconductor detector based on S3590 type Si-PIN-PD.Fig. 2 shows the amplitude spectrum of 226Ra alpha-particles obtained using Si-PIN SCD with the input win-dow of  25 mm diameter.  The  resolution  at  alpha-line with Eα = 7.687 MeV was Rα = 1.7%.Counting rate,R.U.1002003004000 200 400 600 800Ra22688 4.602Ra22688 4.785Po21084 5.297Rn22286    5.490Po21884 6.003Po21484   7.687R=1.7 %226RaChannel numberFig. 2. Spectrum of 226Ra alpha-particles obtained using a NPO «BIT» semiconductor detector of Si-PIN-PD type. Figures at the total absorption peacs denote the energy of alpha particles in MeV.Spectra due to 109Cd, 137Cs and 207Bi ICE obtained us-ing a ZnSe(Te) based detector  of 9x9x1 mm3 size to-gether with an S3590 Si-PIN-PD are shown in Fig. 3.Channel numberCounting rate, R.U.500100015000 100 200 300207Bi1002000 100 200 3002004006008000 100 200 300 400 500 600109CdEL=84.68 keV137CsEК=62.52 keVEK=624 keVEL=645 keVЕγ 2=1063keVЕL=1048keVЕγ 1=569.7keVEК=976keVRe=3,7%ЕK=481.1 keVЕL=554.4 keV ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 174-176.175Fig. 3. Spectra of 109Cd (Еγ=85,03 кэВ), 137Cs (Еγ=662 keV), 207Bi (Еγ1=569,7 keV and Еγ2=1063 keV) internal conversion electrons obtained using a ZnSe(Te)-based detector of 9x9x1 mm3 size and an S3590 Si-PIN-PD.In Fig. 3,  one can distinctly  discern the  109Cd ICE L-line (EL1 = 84.23 keV,  EL2 = 84.68 keV). The K-line due to 109Cd ICE (EK = 62.52 keV) is not clearly seen at the background of noises, presumably because of ICE energy losses in the “dead” surface-adjacent crystal lay-er.  This  is  confirmed by the data presented in  Fig. 3. The  241Am gamma-line  with  Eγ = 59.6 keV is  clearly discerned at the background of detector noises. Turning back to Fig. 2, one should note that detection of  137Cs ICE allows in  principle resolution of  K- and L-series ICE with  Ee of 624 and 645 keV. The  207Bi spectrum shown in Fig. 2 gives clear resolution of ICE and gam-ma-lines.Spectra of  241Am gamma-quanta and of 239Pu alpha-particles obtained using the above-described ZnSe(Te) based detector of 9x9x1 mm size in combination with S3590 Si-PIN-PD are shown in Fig. 3.Channel numberCounting rate, R.U.1000200030000 100 200 300 4002004006008000 100 200 300 400 500 600 700 800241AmEγ =59.5 keV90Sr501001500 100 200 300 400 500 600 700 800239PuEα =5150 keVGeneratorRα =3 %FWHM=63 keVFWHM=155 keVЕα =5486keVFig. 4. Spectra of 241Am gamma-quanta, 90Sr beta-particles and 239Pu alpha-particles obtained using a ZnSe(Te) based detector of 9x9x1 mm size and an S3590 Si-PIN-PD.Alongside the  239Pu alpha-line with  Eα = 5150 keV, the 241Am alpha-line with Eα = 5486 keV was observed. 231Am is formed as a result of 241Pu beta-decay, which is present in the alpha-source as an admixture. The energy resolution of the detector for 5150 keV alpha particles is Rα = 3% (Fig. 4). The intrinsic resolution value  Rα for the ZnSe(Te) crystal was determined according to the expression,RRR 2p2d −=αwhere Rd is the resolution of the detector-CSPA system for 155 keV alpha-particles, and  Rp is the resolution of the system involving the detector capacitance and CSPA with  the  pulse  generator  (63 keV).  Hence Rα = 141.6 keV, or Rα = 2.75%, which is not worse than with the best CsI(Tl) crystals in combination with PMT.The energy resolution of the ZnSe(Te) – Si-PIN-PD detector for  207Bi ICE (Re = 3.7%) is essentially better than  with  plastic  scintillators  combined  with  PMT (5-7%). The α/β ratio for ZnSe(Te) crystals is ~1, which is  substantially  higher  as  compared with alkali  halide and oxide scintillators.Our  further  studies  of  “fast”  ZnSe(Te)  scintillator crystals  (which  had  been  also  produced  at  STC  RI) showed that  the energy resolution  Rγ for  detectors  of “ZnSe(Te) – avalanche photodiode” for  gamma-radia-tion with Eγ = 662 keV was ~5.4 %, with intrinsic value of Rγ being about 3.3 % [3].4  CONCLUSIONSStudies of spectrometric characteristics, which were carried out for combined detectors based on Si-PIN-PD and ZnSe(Te) crystals, show that such detectors can be promising for applications in spectrometry of charged particles.Our results for α/β ratio, as well as resolution values Rα, Rβ, Rγ, show that these detectors, taking into account their  high  thermal  and  radiation  stability,  are  very promising, especially for detection and identification of fission products of various radioactive materials in ex-treme conditions.This  work  is  supported  by  the  INTAS  Grant No 99-01348.REFERENCES1.J.Friese  et  al.  The  SISWICH,  a  Detector  Telescope with  Intrinsic  Calibration  //  IEEE  Trans.  Nucl.  Sci. 1993, v. NS-40, N. 4, p. 443-446.2.L.V.Atroschenko,  S.F.Burachas,  L.P.Gal’chinetskii, B.V.Grinev,  B.D.Ryzhikov,  N.G.Starginskii.  Crystals  of  scintillators  and detectors of  ionizing radiation on  their base. Kiev: Naukova dumka, 1998, 310 p.3.M.Balcerzyk, W.Klarma, M.Moszynski et al. Nonpro-portionality and temporal response of ZnSe(Te) scintil-lators studied by large area avalaunche photodiodes and photomultipliers //  Scientific Program and Abstracts of  the Fifth International Conference on Inorganic Scintil-lators  and  Their  Applications  “SCINT  99”,  P1-5, ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 174-176.176Moscow State University, Russia. 1999, p. 125. ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.Серия: Ядерно-физические исследования (39), с. 174-176.177

Combined detectors of charged particles based on zinc selenide scintillators and silicon photodiodes

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Combined detectors of charged particles based on zinc selenide scintillators and silicon photodiodes

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